1. Field of Invention
This invention relates to devices for reducing the pollution created by an engine of a motor vehicle and more particularly, to apparatuses for preventing the discharge of evaporated fuel gas into the environment from a motor vehicle.
2. Prior Art
Conventional devices for preventing the discharge of evaporated fuel gas consist of a charcoal canister made of activated charcoal which absorbs and temporarily stores evaporated fuel gas, a purge port which is placed inside the intake passage of a carburetor of the engine and a passage for evaporated fuel connecting the purge port with the charcoal canister. When the engine is operated, evaporated fuel which has been stored in the charcoal canister is sucked out into the air intake passage by means of a negative pressure and is burned in the engine.
When it becomes necessary to purge a large quantity of evaporated fuel gas by means of a conventional device for preventing the discharge of evaporated gas described above, the cross section of the purge port mentioned above must be enlarged in order to increase the flow rate. An increase in the cross section of the purge port, however, gives rise to various difficulties. When the canister is fully loaded with evaporated gas to a level near saturation, especially at the time of starting the engine, the mixed gas becomes overly rich. On the other hand, when the canister is in a sufficiently purged state, at a time of ordinary driving, the mixture of gases becomes too lean and this affects the operation and capability of the engine.